Plunger pumps have been used for a wide variety of metering applications, particularly those involving low flow rates. The volumetric delivery of such pumps can be affected by various factors. The presumed volume delivered by such pumps is calculated based on the displacement per revolution. However, if the cylinder does not fill completely and efficiently during the intake stroke, the precise amount delivered is not capable of accurate measurement.
Some liquids are so viscous that a booster force must be applied to the liquid in its storage container in order to move the material through the suction lines and into the cylinder.
Due to the wide variety of liquids that are pumped through plunger pumps, further inaccuracies can result if the material has varying physical properties with temperature, which may affect its viscosity, and if the material is compressible to any degree.
Dead spots are particularly undesirable in the construction of plunger pumps since vapors such as air may accumulate in those dead spots which, depending upon the volume, may prevent the pump from pumping at all. In some designs, the dead volume substantially exceeds the total displacement volume and this can prevent the pump from purging itself while it is operating.
Frequently, when it is time to maintain such pumps, the piping must be disconnected from the pump body so that work can commence on renewing or replacing the check valves. The check valves are a part that requires more frequent maintenance among the various pump parts. Several known designs incorporate the check valves in a manner that requires disassembly of the suction and discharge piping to obtain access for maintenance. Typical of such plunger pump designs are U.S. Pat. Nos. 3,801,234; 4,854,835; 4,269,572. Other references address the issue of the need to remove the valves easily but provide fairly complicated solutions for their removal. Such patents include U.S. Pat. No. 4,618,316. Yet other designs feature complicated internal passages among various cylinders, such as U.S. Pat. No. 3,746,476. Yet other designs still require disassembly of the suction and/or discharge piping for full and ready access to the complete suction and/or discharge valve assemblies or for maintenance of the relief valve. Typical of such patents are U.S. Pat. Nos. 4,477,237 and 4,778,347.
The apparatus of the present invention seeks to provide a design for a plunger pump wherein the suction and discharge valves are easily accessible without disassembly of piping. The design further seeks to embody a built-in relief valve which is easily accessible without removal of any piping and which is fully internally ported from the discharge piping to the suction piping. The design further seeks to eliminate as much as possible any dead spots and to provide a means for elimination of air which may be trapped in such dead spots which could possibly prevent the pump from pumping.